Outlook 2007: Outlook prompting for password issue

Symptoms: Outlook 2007 clients are prompting for password when connecting to Exchange 2007.

Possible solutions if affecting single users:

• Open the profile settings and make sure there is no checkbox in "Always prompt for user name and password" on the Security tab
• Check credential manager. It may be storing an incorrect password for the user and Outlook may be using this to connect to Exchange. Run control userpasswords2. On the Advanced tab, select "Manage Passwords". Remove any entries to the Exchange server. Alternatively, erase the server name and enter "S1" or the simple name of your global catalog server and leave the password blank. If prompted again, enter your username and password and check off "remember my password" one last time and it should not prompt again.
• Try typing in the username by including the domain name. i.e. DOMAINNAME\Username. This has been known to resolve the issue.
• In the task tray, hold down CTRL Key and right click the Outlook icon and select Test Email Auto Configuration. Uncheck Use Guessmart and Secure Guessmart Authentication. Click Test. When the test is completed, view the XML results.
• Check that the autodiscover URLs are in the proxy exceptions list.
• Open the following path: In Vista: \Users\YourUserName\AppData\Roaming\Microsoft Once open you will see numerous folders including a “protect” folder. Delete the “protect” folder. When you have deleted the protect folder, restart Outlook. You will be requested to enter your password again, but it will be the last time.
  Check that an Internet security product is not blocking a port.

Possible solutions if affecting a large number of people:

• Open IIS on theExchange server and checked the following directories under the default website: the root site, oab, autodiscover. Under the directory security tab, click Edit in the Secure Communications section. If you have "require SSL" checked and the 128 bit encryption, but under Client Certificates, it is set to ignore, then this may be the problem. Change this to "Accept" for each of the folders and restart IIS. This may not be a satisfactory solution for everyone.
• Try to connect to the autodiscover URLs listed in the SCP and in Exchange Management Console.
• Make sure the OABurl is set to https and not http
• In the task tray, hold down CTRL Key and right click the Outlook icon and select Test Email Auto Configuration. Uncheck Use Guessmart and Secure Guessmart Authentication. Click Test. When the test is completed, view the XML results. If the URL for the OAB is starting with HTTP instead of HTTPS then you may need to change this from the Exchange Management Console. Do an iisreset and test again.
  Make sure integrated security is enabled on the virtual directories where required.
• Ensure Offline Address Book has been migrated to Exchange 2007.
• Look at the properties of the autodiscover virtual directory and ensure a version of ASP is selected. If none is selected, clients may be prompted for password.
• Ensure Windows authentication is enabled on the Autodiscover virtual directory.
• See http://support.microsoft.com/kb/236032

If the problem exists when using RPC over HTTP:

If you are working RPC over https you are using or basic, or NTLM authentication, you need to be sure you are working NTLM. Now in order to ensure that outlook not uses any cached password we need to do the following. Go to Control Panel>User AcountsPress on Advanced Tab button. Click on Manage Passwords button. Review stored passwords , and if you see IP address of your mail server you should delete it.
Now we need to patch te registry
Click StartRun
Type regedit and press enter
Go to HKLM\SYSTEM\CurrentControlSet\Control\Lsa\
Find lmcompatibilitylevel DWORD parameter
Double-click on it and change its value to 3